Heat exchange is important to ensure machinery and engines such as gas turbine engines remain within acceptable operational parameters as well as to achieve efficient thermodynamic operation. In the field of gas turbine technology, a great deal of effort has been directed toward improving thermodynamic efficiency by operating gas turbine engines at increasing temperatures. As such, numerous heat exchange systems have been developed for directing heat within an engine to components where such heat is beneficial to the operating performance of the engine, while other heat exchange systems have been developed for directing heat away from engine components that normally cannot tolerate such high temperatures.
In one example, a class of heat exchange systems known as recuperators have been developed to recover heat from the engine exhaust, which is otherwise wasted energy, and redirect the recovered engine exhaust heat to the combustion portion of the engine, to increase its overall efficiency. Specifically, the recuperator transfers some of the waste heat in the exhaust to the compressed air that enters the combustion portion of the engine, thus preheating it before entering the fuel combustor stage. As the compressed air has been pre-heated, less fuel is needed to heat the compressed air/fuel mixture up to the desired turbine inlet temperature. By recovering some of the energy usually lost as waste heat, the recuperator can make a gas turbine engine significantly more efficient.
In another example, cooling air may be provided to various turbine engine components using cooling air extracted from other parts of the engine. For example, in some gas turbine engines, cooling air is extracted from the discharge of the compressor, and is then directed to certain portions of the turbine. During some operating conditions, the air that is extracted from the engine for cooling may be at temperatures that require the air to be cooled before being directed to the particular component requiring cooling. To achieve the required cooling, cooling air may be directed through one or more heat exchangers within the engine.
Recuperators, cooling air heat exchangers, and other heat exchangers employed in gas turbine engines have been conventionally designed using either plate-fin architectures or tubular architectures. Plate-fin architectures, while relatively inexpensive to manufacture, do not result in favorable weight and performance characteristics. Tubular architectures, while relatively more efficient than plate-fin architectures, are often prohibitively expensive to manufacture. Furthermore, conventional plate-fin and tubular architectures are susceptible to thermo-mechanical fatigue (TMF), especially at braze connections, as they do not allow adequate thermal growth and stress compliance during transient and steady state operations, reducing their service life and/or necessitating costly repairs. For example, heat exchanger tubes in conventional heat exchangers with tubular architectures may be rigidly coupled to each other by fins or otherwise, thereby restricting relative motion and inducing detrimental stresses in the heat exchanger.
Hence, there is a need for unitary heat exchangers having integrally-formed compliant heat exchanger tubes, and heat exchange systems including the same. There is also a need for unitary heat exchangers having integrally-formed compliant heat exchanger tubes and heat exchange systems having improved efficiency, reduced manufacturing costs, and increased operating lifespan over conventional heat exchangers, with less fluidic loss for improved engine cycle performance, and less weight.